FIG. 1 is a schematic diagram of an overall architecture of a Long Term Evolution (LTE) system in the related art. As shown in FIG. 1, the LTE architecture includes: a Mobility Management Entity (MME), a Serving GetWay (SGW), a user equipment or terminal (UE) and base stations (eNodeBs, short for eNBs). An interface between the UE and the eNB may be an UU interface. An interface between the eNB and MME may be an S1-MME (S1 for the control plane) interface. An interface between the eNB and the SGW may be an S1-U interface. Interfaces between the eNBs may be X2-U (X2-User plane) and an X2-C (X2-Control plane) interfaces.
In the LTE, a protocol stack of the S1-MME interface, from the bottom to up, is divided into the following several protocol layers: an L1 protocol, an L2 protocol, an Internet Protocol (IP), a Stream Control Transmission Protocol (SCTP) and an S1-Application Protocol (S1-AP).
In the LTE, a protocol stack of the S1-U interface, from the bottom to up, is divided into the following several protocol layers: an L1 protocol, an L2 protocol, a User Data Protocol (UDP)/IP, and a General Packet Radio Service (GPRS) Tunneling Protocol-User Plane (GTP-U).
At present, as the frequency spectrum resources are in short supply and the large-traffic services of a mobile user surge, in order to increase the user throughout and enhance the mobile performance, the demand of adopting a high frequency point such as 3.5 GHz to perform hotspot coverage is increasingly obvious and a node with a low power becomes a new application scenario. However, the signals of the high frequency point are attenuated sharply, and the coverage range of a new cell is relatively small and there is no common site between the new cell and the existing cell. As a result, if the user moves among these new cells, or moves between the new cells and the existing cells, a frequent switching process is undoubtedly caused such that user information is frequently transferred among the base stations and thus a huge signaling impact is brought to a core network. In view of this, it is curbed to introduce a large number of small cellular base stations at a wireless side.
FIG. 2 is a schematic diagram of an overall architecture of a small cellular base station system. As shown in FIG. 2, the architecture includes an MME, an SGW, an UE, a master base station eNB (MeNB), and a secondary base station eNB (SeNB). An interface between the UE and the base station may be an UU interface. An interface between the MeNB/SeNB and the SGW may be an S1-U interface. Interfaces between the eNBs may Xn interfaces, The user data may be sent to the user from the core network by means of the MeNB, and also may be sent to the user from the core network by means of the SeNB. Upon access of the user to the MeNB, dual links may be implemented by adding, modifying and deleting the SeNB.
Meanwhile, with extensive requirements of the user to a local service and an internet service, the UE and the core network supports an always online function. That is, after a data link is established, the UE may send the data to an external data network at any time, and the external data network also may send the data to the UE. Herein, the external data network refers to an IP network that does not pertain to a Public Land Mobile Network (PLMN) and has a connection with the PLMN, for example, it may be a home inner network or an internet. We also call the function as a Local IP Access at Local Network (LIPA@LN) or Selected IP Traffic Offload at Local Network (SIPTO@LN) function. If a Local GateWay (L-GW) supporting an LIPA or SIPTO service is arranged on the base station (it also may be a macro base station or a home base station), we call it as a collocated L-GW. The system architecture supporting the SIPTO@LN and the collocated L-GW is as shown in FIG. 3.
Under the existing LTE system, to achieve the SIPTO@LN or LIPA@LN function, in a scenario of the collocated. L-GW, the base station where the collocated L-GW is located needs to report an IP address of the L-GW to the core network by means of a UE dedicated message, such that a Packet Data Network Gateway (PDN GW) for the SIPTO/LIPA service selects to use the address provided by the (H)eNB but not the Domain Name Server (DNS) query, Hence, there is a need for the base station to carry the IP address of the L-GW in an INITIAL UE MESSAGE (sent to the MME and used for security authentication of a Non-Access Stratum (NAS) layer between the network and the UE) and an UPLINK NAS TRANSPORT message. In the above small base station system, since the concepts of the MeNB and the SeNB are introduced, when a cross MeNB switching is performed by the user under the small base station environment, if the base station where the L-GW is located is the SeNB, it is necessary to consider the impact of a switching process on the SIPTO/LIPA service.
An effective solution has not been proposed yet at present for the problem of not considering the processing of the SIPTO/LIPA service in the cross MeNB switching process in the related art.